PROJECT SUMMARY: Pathology?determining the causes and effects of disease, often by using a microscope to examine patients' tissue?is essential for arriving at a correct cancer diagnosis, but it has become increasingly important to submit relevant portions of often tiny tissue samples for DNA and other molecular and functional tests. Making sure that the submitted material actually contains tumor, in sufficient quantity, is not always easy, and sometimes just preparing conventional microscope slides can consume most or even the entire specimen. We have developed a new, simple and inexpensive approach we term MUSE, for Microscopy with UV Surface Excitation, that can provide high-resolution images directly and quickly from fresh tissue without consuming it, and thus can preserve intact, high-quality specimens for biobanking, downstream molecular and functional analyses. MUSE, by ensuring that acquired small biopsy specimens are indeed fit for purpose, can avoid the need to have a patient return at a later date for additional biopsies. In addition, the method will allow for lesion detection over larger cross-sections of tissue, such as organ whole-mounts, not currently practical with conventional instrumentation. Finally, we expect that MUSE will yield additional biologically informative imaging by avoiding artifacts inherent in conventional tissue processing and sectioning. We focus here on facilitation of tissue-based molecular studies, viable tumor harvest for xenografts and cultured spheroids, and biobanking, and include crucial validation studies to ensure that the MUSE process does not compromise sample utility due to possible impacts from exposure to intercalating dyes and/or UV light. MUSE relies on two mechanisms: 1) surface-restricted excitation of fluorescent dyes due to micron- scale penetration of sub-300-nm ultraviolet light; and 2) the fact that many conventional dyes excited in this way emit visible light. These signals are bright enough to be detected by conventional color cameras using sub-second exposure times, allowing rapid imaging of large areas. MUSE eliminates any requirement for conventional histology processing with formalin fixation, paraffin embedding, or thin-sectioning. It requires no lasers, confocal, multiphoton or optical coherence tomography instrumentation, can eventually cost in the range of a few thousands of dollars, and therefore affordable at the point of care (point of biopsy). MUSE samples are stained within seconds using familiar histology stains, such as eosin and DAPI, and the resulting high-resolution images converted from fluorescence to H&E-like brightfield appearance for interpretation in real time (but with novel and potentially useful features) easily interpreted by pathologists. While rapid cellular-scale imaging of fresh tissue can have significant benefits in clinical arenas, it can also empower basic and translational research use for essentially instant histology-, pathology- or toxicology-relevant images directly from experimental animal models?at the bench?and may help relieve such investigators from having to rely on often overworked, sometimes unavailable, conventional histology and pathology services.